1. Field of the Invention
The present invention relates to a linear measuring machine having a vertically elevatable probe to touch a target portion of a workpiece to measure a dimension of the workpiece such as height, step, hole and shaft.
2. Description of Related Art
For measuring a dimension of a workpiece such as height, step, hole and shaft is measured on a surface plate, a linear measuring machine having a vertically elevatable probe, so-called height gauge is used.
Among the height gauge, a motor-driven type height gauge has a base movable disposed on a surface plate, a column standing on the base, a slider elevatable along the column and having a probe, an elevation driving mechanism including a motor for elevating the slider, a displacement sensor for detecting a displacement amount of the slider in height direction, a display, and a controller for elevating the slider by driving the elevation driving mechanism based on a measurement command, for fetching a detection value of the displacement sensor when the probe touches the measurement surface of the workpiece, and for displaying the detection value on the display.
In the motor-driven type height gauge, when a certain measurement item is commanded for measurement, the controller raises or lowers the slider by driving the elevation driving mechanism. When the probe touches the measurement surface of the workpiece by lifting or lowering the slider and a fluctuation value of vertical position is below a predetermined level, the detection value of the displacement sensor is fetched, which is displayed on the display.
Accordingly, an operator can measure the height position of the measurement surface of the workpiece onto which the probe touches by the detection value (measurement value) displayed on the display.
Incidentally, since the probe keeps on touching the workpiece once the probe touches the workpiece, in order to conduct the next measurement, the operator moves the probe in a direction away from the workpiece (upward or downward) for a predetermined degree to draw out the probe from the workpiece before the next measurement.
If the measuring machine and/or the workpiece are moved immediately after measurement without the above operation, since the workpiece and the probe moves while keeping interference therebetween, i.e. the workpiece and the probe are in contact with each other during movement, the workpiece can be scarred or the probe may be damaged.
An object of the present invention is to provide a linear measuring machine capable of avoiding scar on the workpiece or damage on the probe even when the measuring machine and/or the workpiece are moved immediately after the measurement, i.e. to provide a linear measuring machine capable of improving measurement efficiency without causing damage to the workpiece and/or the probe.
For attaining the above object of the present invention, the linear measuring machine according to the present invention has following arrangement.
A linear measuring machine according to the present invention includes: a base movably disposed on a surface plate; a column provided on the base; an elevation driving mechanism including a motor for lifting and lowering the slider; a displacement sensor for detecting a displacement of the slider in a height direction; a controller for fetching a detection value of the displacement sensor when the probe touches a measurement surface of a workpiece; and a display for displaying the detection value fetched by the controller. The linear measuring machine is characterized in that the controller has a touch-and-back mechanism for moving the elevation driving mechanism in a direction away from the measurement surface of the workpiece after fetching the detection value of the displacement sensor when the probe touches the measurement surface of the workpiece and for stopping the slider, when the slider is lifted or lowered by driving the elevation driving mechanism.
In the above arrangement, the controller lifts or lowers the slider by driving the elevation driving mechanism when a measurement command is given. When the controller detects that the probe touches the measurement surface of the workpiece by lifting or lowering the slider, the controller drives the elevation driving mechanism in a direction for the probe to move away from the measurement surface of the workpiece after the detection value of the displacement sensor at that time is fetched. Accordingly, since the workpiece and the probe are separated in the above condition, the workpiece is not scarred or the probe is not damaged even when the measuring machine and/or the workpiece are moved immediately after the measurement. Accordingly, the measuring machine and the workpiece are not damaged and measurement efficiency can be improved.
In the above, the touch-and-back mechanism may preferably stop driving the elevation driving mechanism when the probe is retracted to reach a predetermined allowable stop area relative to a retraction target position remote from the measurement surface of the workpiece by a predetermined retraction amount.
According to the above arrangement, since the drive of the elevation driving mechanism is stopped when the probe is retracted to reach the predetermined allowable stop area relative to the retraction target position, the probe is stilled adjacent to the retraction target position by inertia. In short, the probe can be stilled at a position adjacent to the retraction target position.
In the above, the touch-and-back mechanism may preferably forcibly stop the slider when the probe keeps on retracting beyond the retraction target position and when a predetermined time passes after the probe is separated from the measurement surface of the workpiece.
Accordingly, since the slider is forcibly stopped after the predetermined time even when the probe keeps on retracting beyond the retraction target position, the probe and the workpiece are less likely to interfere with each other.
In the above, the retraction amount may preferably be set at will.
Accordingly, since the retraction amount can be set at will in accordance with the portion of the workpiece to be measured, the interference between the probe and the workpiece can be prevented.
In the above, the touch-and-back mechanism may preferably stop driving the elevation driving mechanism when the probe is retracted to a measurement initiation position if the retraction amount is larger than a distance for the probe to touch the measurement surface of the workpiece from the measurement initiation position.
Accordingly, since the elevation driving mechanism is stopped when the probe is retracted to the measurement initiation position if the retraction amount is larger than a distance for the probe to touch the measurement surface of the workpiece from the measurement initiation position, the interference between the probe and the workpiece can be prevented in advance.
Alternatively, the touch-and-back mechanism may preferably actuate a brake mechanism before a retraction target position after retraction of the slider.
According to the above arrangement, since the brake is actuated before the retraction target position after the retraction of the slider, the slider can be stopped at an early stage and the interference between the probe and the workpiece can be prevented in advance.